We will take a genetic approach to dissect the neuronal circuitry that underlies behavioral aversion of UV, using the Drosophila egg-laying site as our model system. We aim to identify and characterize both the critical sensory neurons and their post-synaptic targets that govern UV aversion. In addition, we will also assess the roles of neuro-modulatory neurons in adjusting the strength of UV aversion via modulating the communication between the specific sensory and central neurons we identified.